Validation and Sensitivities of Dynamic Precipitation Simulation for Winter Events over Folsom Lake Watershed: 1964-99

1. Validation and Sensitivities of Dynamic Precipitation Simulation for Winter Events over the Folsom Lake Watershed: 1964–99 Jianzhong Wang and Konstantine P. Georgakakos Monthly Weather Review: Vol. 133, No. 1, pp. 3–19.

2. 1964–99 (62 winter enents) • CNRFC 1964 - 1999 • SCPP 1980 – 1986 • MM5 achieves a good percentage bias score of 103% • spatial grid resolution higher than 9 km is necessary • the model performs better for heavy than for light and moderate precipitation

3. Introduction • the measurement and prediction of its spatiotemporal distribution are necessary prerequisites • the scarcity of the precipitation sensors • it difficult to delineate finer-scale characteristics of precipitation distribution • National Research Council 1988 , 1991 , 1995 ; Sharratt et al. 2001 ; Georgakakos 2003 ; Smith 1979 ; Pandey et al. 2000 ; Hevesi et al. 1992 ; Tsintikidis et al. 2002 • Use CNRFCSCPP data validate the precipitation simulations of MM5 • the statistically significant sensitivities of the numerical simulation to model initial and boundary forcing, and microphysical parameterization

4. studies reported • Colle and Mass (2000) • Colle et al. (2000) • Vellore et al. (2002)

5. goal • to study how well dynamical precipitation simulation reproduces observed features of precipitation for the Folsom basin on a subbasin scale for light, moderate, and heavy precipitation • to study the factors that affect simulation accuracy for precipitation on hydrologic basin scales • shortcomings of implicit and explicit cloud and precipitation parameterization schemes are also responsible for low simulation skill

7. Precipitation events and data • 1958 NCEP reanalysis I 1999 • 1964 NCEP reanalysis II 1999 • I 1979 II 1999* • 1995 1999 • Eta 40km 3-h • 1986 SCPP 1986 • 1968 CNRFC 1999

8. the spatial averaging × × × × × × × × × × × × × R

9. Why grid box • the model-simulated precipitation itself is a simulation of mean areal precipitation over the grid area and not a single point value • the MAP, estimated from either model grid points or single-point observations, has less variance and allows better comparisons • single-point precipitation measurement is quite often not representative of the volume of precipitation falling over a given catchment area

10. CNRFC operational stations

11. During SCPP period (denser pbserving network)

15. One way nesting Resolution is 81,27,9 km;91x91x23;Goddard graupel ,KF

17. 47 cases overestimate

24. Concluding remarks • The model simulates best heavy-precipitation events and overestimates MAP consistently for light- and moderate-precipitation events. • spatial model resolution down to 3 km and a denser observation network may be necessary • the precipitation overestimation by the model in the upslope of the Sierra Nevada is reduced significantly from 26% to 3%(CNRFCSCPP)----more accurate estimation of the true MAP • MM5 to underestimate (overestimate) the actual MAP for most of the heavy (light to moderate) winter precipitation events

25. the 40-km Eta analysis data has a statistically significant advantage over the 2.5° NCEP reanalysis data at the 80% confidence level • The average event-total basin MAP model is also found sensitive to the MM5 cold microphysicsschemes used, but this sensitivity was less than that due to changes in model initial and boundary fields • MM5 provides reasonable average event-total MAP simulations for the 4280-km2 Folsom basin, especially for heavy-precipitation events and with operational Eta analysis providing initial and boundary fields • lend credence to analyses of mesoscale atmospheric circulation, hydrologic cycle effects, and microphysical effects that are based on MM5 dynamical simulations of heavy upslope precipitation events in the region

27. bias